The present invention relates in general to the control of material flow through an opening by means of a moveable sealing disc, and more particularly, to a linearly actuated valve of the pseudo-gate type having a sealing disc rotatable during use to affect uniform distribution of wear over its sealing surfaces thereby substantially increasing its useful life. Still more particularly, the present invention relates to valves of the sliding-gate or disc type which are especially well suited for controlling the flow of highly abrasive materials such as slurries and the like.
It is well known in the material handling art to employ sliding-gate or disc type valves for the purpose of controlling material flow. A conventional moveable gate or disc will reciprocate between an open position allowing material flow to a closed position wherein the gate or disc moves against a valve seat to close off material flow. In the course of normal use, the valve seat typically becomes eroded, worn and/or corroded as a result of this continued action.
Various attempts have been made to improve this valve operation by overcoming or avoiding the deterioration of the valve seat. It has been proposed to provide removable valve seats which may be replaced without replacing the entire valve, such as known from Grieves, et al., U.S. Pat. No. 4,429,710. Other attempts have included the use of movable valve seat protectors which selectively cover the valve seats, such as known from Almada, U.S. Pat. No. 4,949,939. In all, these gate valves have been found to be unsatisfactory, in that breakdown or removal of the valve seat often still requires replacement of the entire valve.
In an effort to overcome the adverse effects of valve seat wear, there is known the various designs of a rotating disc valve. In this regard, the sealing discs are arranged for limited rotation about their supporting shafts during each opening and closing cycle of the valve. One such rotating disc valve is available from Everlasting Valve Company, Inc. of South Plainfield, N.J., the assignee of the present invention. In operation, an actuator moves a valve stem and lever arm a quarter turn, which drives a sliding sealing disc. The entire sealing surface of the disc is constantly in contact with the valve seat through force exerted by coiled springs which allow the disc to move vertically. This compensates for thermal expansion and contraction of the valve's components, also overcoming the effect of any backpressure for which it was designed and prevents particles from lodging between the sealing surfaces. Differences in tangential disc to seat friction forces causes the disc to rotate on its seat as the valve cycles, thereby shearing and wiping away any processed materials it may have accumulated. Rotation of the disc produces an action that in the process medium renews and polishes the metal seating surfaces with each operation. Rotating disc valves of this general type are also known from Krakovsky, U.S. Pat. No. 4,373,546.
In the Krakovsky and Everlasting rotating disc valve, the disc is moved along a curved path by the pivotal operation of the actuator and lever arm. This pivotal arrangement has necessitated an undesirable size configuration of the valve housing to accommodate the extent and location required for the valve actuator operation. It has been found that this design in certain applications, for example steam isolation valves, will not meet the size requirements of an economically and technically competitive cast valve body. To this end, there is known from Uomala, U.S. Pat. No. 4,367,766 and Krakovsky, U.S. Pat. No. 4,449,547, a linearly actuated disc valve which employs a straight line motion of the sealing discs. Uomala discloses a gate valve having a linearly actuated valve spindle supporting a T-joint. Rotatably mounted on either face of the T-joint is a circular sealing disc journaled by means of a ball. A pair of flexible pins are arranged extending from within a cover of the valve housing. As the valve spindle raises the sealing discs, the pins circumferentially engage the sealing discs to cause limited rotation thereof.
In Krakovsky, a similar gate valve having a pair of sealing discs mounted for rotation on respective bearings are moved by means of the linear movement of a valve spindle. The size of the fluid inlet opening is greater than the size of the outlet opening in order to create a variable fluid flow through the valve which is affected primarily by the position of the sealing disc relative to the outlet opening. The outlet opening may be symmetrical in shape or otherwise asymmetrically located relative to the closure path of the center of the disc. Fluid flow through the valve produces a rotational torque on the sealing disc about the center of its bearing to rotate the disc whenever the friction between the disc and its seat is not significantly great from the wedging action during closing of the valve.
These aforementioned valves although providing for linear actuation of a rotatable disc are less than desirable in design and suffer from a number of notable disadvantages. For example, the Krakovsky valve enables only the rotation of one of the two discs during operation, in addition to requiring an undesirable diverted flow path through the valve housing. As to Uomala, the pins are only effective upon complete opening of the valves thereby limiting their utility during valve throttling operations. In addition, the pins are relatively inaccessible requiring disassembly of the valve housing in the event of their breakage.
Accordingly, it can be appreciated that there is an unsolved need for a linearly actuated rotating disc valve which overcomes and avoids the disadvantages and deficiencies of the aforementioned known rotating disc valves.